How to make clouds in cycles?
To model the clouds faster, use the add-on CloudGen that comes packaged with blender. It does the material for you and there are good preset options. If it is taking too long to render, render two shots: Your standard shot with the platform and then another one that is the clouds on a transparent background. Then, you can use the compositor to layer the two shots and if your camera is the same, it should look seamless.